The present invention relates to a T-S (Torque-Stroke) curve correction method for a clutch system, and more particularly, a T-S curve correction method for a clutch system, which is capable of preventing an occurrence of slip by correcting a T-S curve based on differences between actual positions at low and high torques and a position on a T-S curve.
In general, a transmission for transmitting power of an engine includes a clutch which is one of transmission parts and serves to couple a driving shaft engaged with a gear to the engine in order to transmit power, or separate the driving shaft from the engine in order to disconnect power.
In order for the clutch to transmit torque of the engine, the position of the clutch is changed by an actuator such as a solenoid or motor. The torque capacity of the clutch based on a moving distance of the clutch may be expressed as a T-S (Torque-Stroke) curve, and torque transmitted by the clutch based on a moving distance of the clutch may be accurately estimated only when the T-S curved is trained by abrasion, thermal deformation and vehicle deviation.
During clutch control of a DCT (Dual Clutch Transmission), input engine torque may be reliably transmitted to a clutch, only when the relation between clutch torque and stroke, that is, the T-S curve is accurately recognized.
For reference, the DCT includes two clutches connected to two input shafts and one output shaft, unlike a conventional single-disc clutch transmission system. The input shaft indicates a rod-shaped shaft for transmitting power to a predetermined position through a rotational motion or linear reciprocating motion.
The engine is connected to the input shafts by the clutch, and the input shafts are connected to the output shaft through a gear and transmit power to wheels. The clutch is a kind of shaft coupling device which is used to connect or disconnect shafts to or from each other, and temporarily disconnects or connects power of the engine. The clutch is used when the gear is shifted to change speed.
A general 7-speed DCT includes first and second input shafts and first and second clutches. The first input shaft is connected to odd-numbered (1, 3, 5, 7) gears, and the first clutch couples a gear stage to the engine. The second input shaft is connected to a reverse gear (R) and even-numbered gears (2, 4, 6), and the second clutch couples a gear stage to the engine.
While a vehicle is operated in a state where the vehicle is connected to the output shaft by an odd-numbered gear of the first input shaft, gear shifting may be performed by applying an even-numbered gear of the second input shaft and raising the torque of the second clutch at the same time as the torque of the first clutch is removed. At this time, an engaged or coupled clutch (for example, the second clutch) may be set to an on-going clutch, and a decoupled clutch (for example, the first clutch) may be set to an off-going clutch.
When the DCT is controlled, a clutch actuator 110, a gear shifting device 120 and a controller 130 are required as illustrated in FIG. 1. The clutch actuator 110 serves to engage or disengage a clutch, the gear shifting device 120 serves to perform gear shifting by controlling a shift fork of the transmission, and the controller 130 controls the gear shifting device 120 according to a vehicle speed and throttle valve opening degree.
The gear shifting device 120 not only serves to simply perform gear shifting, but also needs to have a pre-select function of performing gear shifting only by switching between the coupling state and decoupling state of the two clutches in a state where gear shift stages belonging to two transmission systems divided into odd-numbered stages and even-numbered stages are engaged one by one at the same time.
Furthermore, the gear shifting device 120 must have an active interlock function of maintaining a transmission lug of a transmission system in a neutral state, the transmission system having no part in gear shifting such that two gear shift stages belonging to the same transmission system are not engaged with each other at the same time. The gear shifting device 120 must be able to provide the above-described basic functions through a simple configuration and structure, and secure stable and reliable operability as well as durability.
As described above, the DCT can reliably transmit input engine torque to the clutch, only when the relation between clutch torque and stroke (T-S curve) is accurately recognized during clutch control. If a clutch torque equal to or more than a normal value is matched with a specific stroke on the T-S curve, an excessive direct-connection shock may occur. On the other hand, if a clutch torque less than the normal value is applied, the engine may be run up.
Furthermore, although the T-S curve was correctly matched at the initial stage, the T-S curve may differ from an actual situation, depending on clutch abrasion, thermal deformation or mass production deviation. In order to prevent an abnormality of the transmission system (or clutch system), for example, an occurrence of slip or gear shifting shock, a difference value between an actual position at low or high torque and a position on the T-S curve needs to be determined in order to properly correct the slope of the T-S curve in the increasing or decreasing direction.
The related art of the present invention is disclosed in Korean Patent Publication No. 10-2015-0070901 published on Jun. 25, 2015 and entitled “Method for correcting clutch characteristic of DCT”.